Epstein-Barr virus (EBV) is associated with several important human malignancies. It is now well established that cytotoxic T lymphocytes (CTLs) play a critical role in controlling the level of EBV-infected B cells which express a family of latent viral antigens, including EBNAs 1,2,3,4,5 and 6. These latent antigens include CTL epitopes that are presented on the surface of virus-infected cells in conjunction with class I antigens. This proposal is designed to assess, for the first time, the capacity of an EBV CTL peptide epitope (EBNA3 derived/HLA B8 restricted) to activate a primary response in vivo in a cohort of human volunteers. These volunteers will be selected from healthy laboratory and army personnel. If successful, this proposal would establish the potential use of synthetic peptides in the development of a subunit vaccine to EBV and to other human oncogenic viruses where it is unlikely that attenuated strains will ever be accepted as a vaccination procedure. The other major aspect of the proposal relates to the mechanisms whereby EBV-associated tumors escape immune surveillance. Particular attention will be focused on Burkitt's lymphoma (BL) which express only EBNA1. Thus far, no CTL epitopes have been localized on EBNA1. The present proposal seeks to demonstrate unequivocally whether EBNA1 includes CTL epitopes. If CTL epitopes are identified in EBNA1, it will be important to determine whether BL cells process and present these epitopes. These studies are designed to delineate how BL cells escape immunological recognition. The methodology to be used in the proposal includes the following: The activation of an EBV-specific response in vivo will be monitored using a standard EBV regression assay, clonal and polyclonal CTL assays and limiting dilution analysis. The sensitivity of BL cells to CTL lysis will be determined following the treatment of tumor cells with appropriate synthetic peptides, vaccinia constructs and transfected episomal viral mini-gene expression vectors. The presence of CTL epitopes within EBNA1 will be assessed by activating an EBNA1-specific response in human and mouse cells using recombinant EBNA1.